Porcelain enamel



res PATE T oral-ice M roncnmm ENAMEL Monroe J. Bahnsen, Lakewood, and Eugene E.

Bryant, Redford, Ohio, assignors to Ferro Enamel Qorporation, Cleveland, Ohio, :2. corporation of Ohio No Drawing. Application October 16, 1949,

Serial No. 361,448 I 15 Claims.

The present invention relates as indicated to porcelain enamels and particularly enamels having high covering power and characterized further in that they contain appreciable amounts of zirconium oxide and that they are free or substantially free of antimony.

- Opaque enamels, i. e., those which have satisfactory covering power and give high reflectance,

as measured by present-daycommercial standards, generally contain substantial amounts of antimony. Antimony-bearing compounds and antimony complexes are generally relied upon to increased at the same time. Commercially available, high opacity enamels in use today are,

' therefore, much more viscous than the enamels impart opacity to enamels for the reason that these substances are white and of a diiierent refractive index than the glass in which they are uniformly distributed. To obtain a high degree of opacity in antimony-bearing enamels, it is necessary to smelt the 'raw batch at as. low, a temperature as possible and still melt the glass to a viscous liquid condition; These enamels thus made under such conditions must be very carefully smelted in order to insure uniform distribution of the antimony-bearing materials throughout the glass body.

The low smelting temperatures used on antimony-bearing glasses are necessary because at higher temperatures there is a tendency for some of the antimony-bearing material to be volatilized and thereby lost and also the remaining antimony-bearing materials dissolved to some extent in the glass matrix and thus lose their opacifying efiect.

As the amount of antimony added in the raw of the past, and can be used today only by very careful control in their manufacture and use.

A furtherdimculty with low firing, high viscosity enamels is their tendency to blister during firing. It has been quite definitely shown that high viscosity and under-smelting. are primary causes of blistering.

It is a principle of this invention, therefore, to provide an enamel characterized by high opacity. Due to the omission of antimony from enamels comprising this invention, they are characterized by high fluidity and are, therefore, more like the clear glasses originally employed as enamels with,

however, the added property of high opacity.

The omission of antimony from the enamel,

also very substantially reduces its cost.,

Other objects of this invention will appear as v the description proceeds.

batch is increased, in order to increase opacity,

the amount of glass-forming materials or fluxes is, of course, proportionately decreased, This also tends toincrease the viscosity of the antimony-bearing glasses during smelting. Commercial practice today utilizes about the maximum possible amount of antimony-bearing materials in the smelter, the upper limit, as indicated, being determined by the difiiculties encountered in smelting.

Accordingly, antimony compounds have been added to the frit as mill additions. The antimony-bearing glasses have also been employed in conjunction with well-known mill additions such as tin oxide, zirconium and titamum compounds,-

as well as various so-called gas or bubble" opaciflers. There is, however, also an upper practical limit to the concentrations inv which these various mill additions may be employed. As indicated, when the opacity of enamel is increased in accordance with conventional methodsin use today, the viscosity of the enamel 1s To the accomplishment of the foregoing and related ends, said invention, then, consists of the steps hereinafter fully described and particularly pointed out in the claims.

The following description sets forth in detail one approved method of carrying out the invention, such disclosedmethod, however, constituting but one of various ways in which the principle of the invention may be used.

Broadly stated, this invention comprises the discovery that by the use of substantial amounts f of phosphorous-containing compounds in zitconium-bearing antimony-free frits and particularly in frits of a relatively narrow range of composition, the frit which, as normally smelted, is a work which has been run in antimony bearing enamels. Y I It has been discovered that additions of small amounts of titanium dioxide or manganese dioxide or mixtures of these two when smelted with the raw batch will greatly. improve the color so that the resulting glass will have essentially the theory on which the results of the present invention are achieved, nevertheless, the action of the.

glass in the smelterduring the annealing stage, above referred to, seems to confirm this conclusion.

As indicated, a frit produced in accordance 'with this invention which, if quickly cooled from a high temperature, is a clear frit or alternatively, if fritted from an annealing temperature is a white frit, will, when deposited in a. conventional; manner and fired on the metallic article, produce a white enamel of unexpected covering power. Thus, for example, when fired on a sheet metal article at a temperature of 1500 F. to 1520 .F., 64 grams persquare foot will have atotal .refiectan'ce of 79%. These results are based on two coats of application over conventional blue ground coat. The above figures give an indication of the remarkable covering power of this enamel, even without the use of any of the many available mill addition opacifiers with which-this enamel may be employed. Since the employment of a small amount of opacifier as a mill addition materials, since our enamel can be advantageto a fineness such that there willbe a 1-8 gram residue on a 200 mesh screen from a 50 cc. same ple at a specific gravity of 1.82.

The gum tragacanth in the amounts specified 1 above as a mill addition is useful for the purpose of giving film strength in the dry bisque.

By the foregoing specified examples of mill additions and particularly opacifiers which may beemployed in conjunction with the enamel of our invention, we, of course, do not intend to be limited to the use of such specifically named ously employed in conjunction with other mill additions and particularly other opacifiers. Thus, for example, We have been able to secure very satisfactory results indeed, by the use of so-called gas or bubble opacifiers and very good results opacifiers and zirconium opacifiers.

examples of gas opacifiers which have been found "useful, we may mention aluminum stearate, aluminum acetate and ethylene glycol.

is desirable from an economic standpoint, it is within the contemplation of our invention to use the enamel of the present invention in conjuncstrength of the dry bisque.

As above indicated, opacifiers are advantageously used as mill additionsin conjunction with this improved enamel and it will be found that best results are secured by the use of the zirconium type opacifier of which there are several at present commercially available.

The compositions of various zirconium opacifiers will be found in the following U. S. patents:

Opacifiers of this character, i. e., zirconium-bearing opacifiers, will generally be found most useful in amounts up to about 5%, since concentrations higher than 5% are generally not as economical as the lower concentrations.

It has also been found advantageous to add one or two pounds of zinc oxide or calcined aluminum oxide to the mill for every hundred pounds of frit used. These materials are added in addition to the usual opacifiers. These additions are helpful in stabilizing maximum opacity and at the same time tend to produce a smoother coating.

' A typical example of a mill addition is as follows:

Per 100 pounds of frit- Clay pounds ,7 /2 Zirconium opacifier do 3 Zinc oxide or aluminum omde do; 1 Potassium carbonate .ounces 6 Gum tragar'anth rlg Water pounds 38 As previously indicated, minor amounts of hentonite, on the order oi 2 oz. per hundred pounds of irit may be advantageously employed on occasion. The frit and the mill additions areground the order of about'68 to 75%. I seen that the present enamel is admirably suited have been secured by the combined use of gas As specific stearate will generally be found to produce best results when employed in concentrations of about 2-3 oz per 100 lbs. of frit; ethylene glycol in the same concentrations, and aluminum acetate 4-5 oz. per 100 lbs. r

Other gas opacifiers which may be used to advantage are those given in U. S. Patent Nos. 1,948,461, 2,102,630, 2,103,228, 2,103,229, and

Our improved enamel may be employed forapplication to either sheet metal or cast iron (either wet or dry process) either a gripcoat or a conventional ground coat being usually employed for best results. The specific formulas given herein are primarily designed for use on sheet steel,

since the compositions as given are inclined to be slightly too hard for use on cast iron. However, the composition may be readily modified to produce a softer firing enamel which may be more suitable for use on cast iron than those above given. As an indication of the very high degree of opacity obtainable by the use of our improved enamel, we might explain that single coat applications of 35-45 gramsper square foot over a conventional sheet steel blue ground coat using approximately 3 lbs. per 100 lbs. of frit of zirconium opacifier as a mill addition and fired at 1500 F. to 1520 F. wiiiproduce refiectances on It will thus be for the production of commercial articles by one cover coat of application.

While it has been indicated above that there may be certain variations made in the composition of the raw mix from which our enamels are produced, it should, nevertheless,- be pointed out 4 our that the zirconium and phosphorus content, as given in the several tables, has been found to be rather critical both as to the amounts employed and the pmportional relationship therebetween. This application is a continuation-in-part of co-pending application Serial Number 311,362, filed December 28, 1939.

Other modes of applying the principle of our invention may be employed instead of the one' explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be em-.

ployed.

Wetherefore particularly point out and distinctly claim as our invention:

1. The method of making. a porcelain enamel Aluminum with said slip and burning the same to form said opaque surface.

Zinc mrirle 2.84

2. An antimony-free opaque vitreous enamel characterized by high fluidity and reflectance when cooled at a relatively slow rate, such characteristics being imparted thereto by the presence therein of phosphorus in an amount made available by the presence of on the order of about 2% to about 3% of P205 and zirconium oxide in an amount equal to about 11% to 14%.

3. A porcelain enamel frit of the character produced by smelting a raw batch mixture comprising about:

Percent Silica sand 0 to 3 Dehydrated borax 15 to 19 Feldspar 22 to 33 Zircon sand 17 to 21 Sodium nitrate 1 to 2 Fluorspar 4 to 8 Sodium fiuo silicate 11 to 17 Bone ash 4 to 6 Aluminum hydrate 3 to 5 Zinc oxide 2 to 3 and at least one of the following within their respective ranges:

Per cent Titanium dioxide Up to 1 Manganese dioxide Up to 1 Borlc acid Up to 8 Calcium carbonate Up to 5 4. A porcelain enamel irit of the character produced by smelting a raw batch mixture the calculated oxide content of which comprises about:

Per cent S10: 29 to 35 ZrOa 11 to 14 B20: 10 to 16 NazO 9 to 13 K20 2 t0 4: CaO 5 to a A120: 7 to 8 ZnO 2 to 3 F2 9 to 13 P205 2 to 3 and at least one of the following within their respective ranges:

Per cent T102 Up to 1 MnOz Up to l.

5. A porcelain enamel frit of the character produced by smelting a raw batch mixture of the following composition:

4 Per cent Dehydrated borax 17.46 F'eldspar 32.50 Zircon sand 20.70 Sodium nitrate 1.22 Fluorspar 4.88 Sodium fiuo silicate 11.38 Bone ash 5.69 Aluminum hydrate 3.25

6. A porcelain enamel frit having a calculated oxide content which is substantially as follows:

Per cent S102 30.56 ZrOz 12.50 B203 12.11 NazO 11.71 &0 2.41 03.0 5.92 A1203 7.41 ZnO 2.58 F2 11.67 P205 2.35 T102 0.72

7. A porcelain enamel irit having a calculated oxide content which is substantially as follows:

Per cent SiOz 29.10 ZrOz 11.91 B203 15.16 NazO 11.15 K20 2.30 CaO 1.44 A1203 7.05 ZnO 2.45 F2 11.11 P205 2.23 MnOz 0.10

8. A porcelain enamel frit or" the character produced by smelting at 2250" a raw batch mixture of the following composition:

Per cent Silica sand 2.82 Dehydrated borax 17.96 Feldspar 24.75 Zircon sand 19.1 1 Sodium nitrate 1.11 Fluorspar 2. w Sodium fluo silicate 16.15 Bone ash 5.26 Aluminum hydrate 4.87 Zinc oxide 2.65 Titanium dioxide 0.80

9. A porcelain enamel frit oi the character produced by smelting at 2250 a raw batch oi the mixture of the following composition:

10. A porcelain enamel slip comprising the enamel of claim 2 and the following mill additions in the amounts specified per pounds of irit:

Clay pounds 7 Zirconium opacifier do 3 Zinc oxide do 1 Potassium carbonate ounces 6 Gum tragacanth do Water pounds- 38 11. A porcelain enamel slip comprising the enamel 01 claim 2 and the following mill additions in the amounts specified per 100 pounds oi. frit:

Clay "pounds-.. 7 Zirconium opacifler do 3 Aluminum nxidp dn 1 Potassium carbonate ounces.. 6 Gum tragacanth do 14, Water pounds 38 12. A porcelain enamel frit oi the character produced by smelting a raw batch mixture comprising about:

Per cent Silica sand 2.84 Dehydrated borax 18.08 Feidspar 24.91 Zircon sand 19.27 Sodium nitrate 1.12 Fluorspar 4.52 Sodium fiuo silicate 16.26 Bone ash 5.29 Aluminum hydrate 4.91 Zinc oxide 2.66 Manganese dioxide 0.14

13. A porcelain enamel frit having a calculated oxide content comprising about:

Per cent Per cent MnO: 0.14

14. A porcelain enamel irit or the character produced by smelting a. raw batch mixture comprising about:

10: sons zrm 12.61 B203 12.19 N520 11.78 K20 2.43 09.0 5.95 A; 7.46 10 2159 produced by smelting a; raw batch mixture, the

calculated oxide content of which comprises about:

Per cent S10: 29 to 35 ZrOz 11 to 14 B20: 10 to 16 NaaO 9 to 13 K20 2 to 4 CaO 5 to A1203 7 to ZnO 2 to F2 9 to 1 P205 2 $0 MONROE J. BAHNSEN. EUGENE E. BRYANT.

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